1. Technical Field
This disclosure relates to the fabrication of magnetic read/write heads that employ TAMR (thermally assisted magnetic recording) to transfer energy from laser radiation to plasmon modes that then enable writing on magnetic media having high coercivity and magnetic anisotropy. More particularly, it relates to the generation of plasmon modes using a plasmon resonator in order to produce field patterns that transfer plasmon energy more effectively.
2. Description
Magnetic recording at area data densities of between 1 and 10 Tera-bits per in2 involves the development of new magnetic recording media, new magnetic recording heads and, most importantly, a new magnetic recording scheme that can delay the onset of the so-called “superparamagnetic” effect. This latter effect is the thermal instability of the extremely small regions of magnetic material on which information must be recorded, in order to achieve the required data densities. A way of circumventing this thermal instability is to use magnetic recording media with high magnetic anisotropy and high coercivity that can still be written upon by the increasingly small write heads required for producing the high data density. This way of addressing the problem produces two conflicting requirements:
1. The need for a stronger writing field that is necessitated by the highly anisotropic and coercive magnetic media.
2. The need for a smaller write head of sufficient definition to produce the high areal write densities, which write heads, disadvantageously, produce a smaller field gradient and broader field profile.
Satisfying these requirements simultaneously could be a potentially limiting factor in the further development of the present magnetic recording scheme used in state of the art hard-disk-drives (HDD). If that were the case, further increases in recording area density might not be achievable within those schemes. One way of addressing these conflicting requirements is by the use of assisted recording methodologies, notably thermally assisted magnetic recording, or TAMR.
If an assisted recording scheme can produce an advantageous medium-property profile to enable low-field writing localized at the write field area, then even a weak write field can produce high data density recording because of the multiplicative effect of the spatial gradients of both the medium property profile and the write field.
The heating effect of TAMR works by raising the temperature of a small region of the magnetic medium to essentially its Curie temperature (TC), at which temperature both its coercivity and anisotropy are temporarily reduced and the magnetic write field required to switch the magnetization of the medium grains is correspondingly reduced as well.
The structure of a TAMR head, in addition to its reading and writing elements, usually includes an optical laser, an optical waveguide (WG) and a plasmon resonator (PR) or plasmon generator (PG). The WG acts as an intermediate path to guide the laser light to the PR or PG, where the optical mode in the WG couples to the local plasmon mode in the PR or the propagating plasmon mode in the PG. After being converted to the plasmon energy either by plasmon excitation in the PR or by plasmon transmission in the PG, the optical energy of the laser is then concentrated at a region of the medium where medium heating and the recording process are to occur. Thus, assuming the heating spot and the magnetic field of the transducer are properly aligned, TAMR recording can be achieved.
Previous methods have utilized an edge plasmon mode to couple to the WG transmitted visible radiation and then concentrated the resulting plasmon energy at the ABS (air bearing surface) of the TAMR head. This approach leads to a smaller thermal gradient than required for certain types of media, particularly in the case of a recording layer with metallic optical properties. Thus, certain types of recording media do not permit the generation of a thermal gradient that will allow the TAMR assist to occur as desired.
Various approaches, such as those taught by:
K. Tanaka et al. (US Publ. Pat. App. 2008/0192376), K. Shimazawa et al. (US Publ. Pat. Appl. 2008/0198496), Shimazawa et al. (U.S. Pat. No. 8,000,178 B2), Jin et al. (U.S. Pat. No. 8,036,069 B1), William Albert Challener (US Publ. Pat. Appl. 2005/0289576 A1), Michael Allen Seigler et al. (US Publ. Pat. Appl. 2009/0073858 A1), Matsumura et al (U.S. Pat. No. 5,712,840), Hongo et al. (U.S. Pat. No. 8,023,365), Matsushima et al. (U.S. Publ. Pat. Appl. 2011/0205865) and Crawford et al. (U.S. Pat. No. 6,954,331) have failed to address the TAMR problem using the method and device to be disclosed below and with the results obtained by that method and device.